[herczegzsolt]

This will be a major inconvenience for migrating mail accounts. I used the POP feature a lot to get mails from one account to the other without requiring a client to do the dirty work.

A migration is still possible, but needing to keep a client up and running to push up mails via IMAP will be a major painpoint.

[xp84]

This sounds like an opportunity for a cool open source project: A container which checks a given POP account every few minutes, and copies the message into an IMAP server of your choice.

[cortesoft]

Someone created that project 29 years ago… fetchmail

https://www.fetchmail.info/

[NetMageSCW]

Google has an email migration feature useful for one time migration.